A great variety of systems for storing and retrieving digital information on a cyclical magnetic storage device such as disc or drum is known in the art. A comprehensive description of various digital data storage methods and addressing thereof can be found e.g. in IBM Manual File No. S-360-30, 1972, Order No. GC26-3746-1; reference is made to pg. 85-101 or in IBM System 360/Operating System, File No. S-360-20, 1971, Order No. GC28-6535-7; reference is made to pg. 34. These prior art systems and methods are designed to store large amounts of digital data but they are not suitable for indexing, storage and retrieval of video information.
A prior art digital data storage and addressing system on a cyclical storage device is described, for example, in the U.S. Pat. No. 3,631,421. In this patent a magnetic disc for storing data and a method of sectoring that disc for addressing purposes is described. The disc has a separate address track on which the more significant digits of the addresses are recorded in binary form. They are compared with the more significant digits of the wanted locations. The less significant digits are compared by a binary counter. The disc has also a separate clock track which serves as a source of reference pulses. The address track is prerecorded permanently and, therefore, it is not suitable for random or indirect addressing purposes. Besides that limitation, two fixed transducer heads are associated with the clock and address track, respectively. This latter arrangement is inconvenient when removing or changing the disc due to necessary alignment of the fixed heads. Furthermore, this prior art storage and addressing system is not suitable for video information storage and retrieval.